Low doses of ionizing radiation, which have little effect on adult mammals, may permanently alter the developing central nervous system of the fetus. The rat model will be used to evaluate the effects of doses between 0 and 1 Gy of gamma radiation(Cesium-137) delivered to the pregnant rat between gestational days 9 and 19. Alterations in the central nervous system will be evaluated at three levels: 1) a series of behavioral tests between parturition and postnatal day 28 will be used to evaluate functional deficits in central nervous activity. These tests include reflex suspension, spatial maze entry, surface righting reflex, activity in a continuous corridor, and specific aspects of the walking gait. In addition, body weight at various times postnatally will also be evaluated. 2) Morphometric analysis of the sensory motor cortex at postnatal day 28 will be performed to evaluate the thickness of the 6 cortical layers. 3) Evaluation of the developing cortex at 0 to 72 hrs post-irradiation in the fetal rat will be conducted to identify the immediate cellular changes that occur in this affected tissue and the time-course for the analyses, functional indices will be acquired gy means of 3H-Thymidine autoradiography, Rhodamine-123 staining to express mitochondrial activity, and potentially other specific metabolic dyes. The data to be acquired will extend our current observations that point to dose-related responses for the behavioral and cortical layer thickness endpoints, and the predictions between behavior and cortical layer thickness. By means of stepwise multiple regression analysis, significant correlations and predictors can be identified that relate early cellular effects to the later development of central nervous system abnormalities. Moreover, predictive analysis can correlate the thickness of specific cortical layers to changes in behavioral test performance. Overall, the information to be gained will contribute to our understanding of a) the specific aspects of the development of the central nervous system in the rat fetus; and b) the effects that low doses of radiation have on these tissues and cells that result in both subtle and drastic alterations in the developing mammalian central nervous system.